Electricity: electrical systems and devices – Safety and protection of systems and devices – Motor protective condition responsive circuits
Reexamination Certificate
2002-12-13
2004-08-10
Riley, Shawn (Department: 2838)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Motor protective condition responsive circuits
C307S010700
Reexamination Certificate
active
06775115
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Application No. 2001-387500 filed on Dec. 20, 2001 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention relates to a voltage conversion system which converts voltage using a converter, a voltage conversion method thereof, and a recording medium that stores a program for implementing the voltage conversion method.
2. Description of Related Art
An inverter has generally been used for driving an alternating current (AC) motor such as a permanent magnet motor. More specifically, direct current supplied from a battery is converted into a desired form of alternating current by means of an inverter and thereafter is applied to a motor to drive it. Especially, in an electric motor vehicle or a hybrid motor vehicle, it is necessary to finely control the output of the motor, therefore such a system using an inverter is preferably used.
In a case that a motor is driven by use of a system including an inverter as described above, however, when an input voltage of the inverter is low, it may cause an undesirable state where current necessarily becomes high to achieve a high output of the motor. In view of this, there is a demand for maintaining the input voltage of the inverter sufficiently high. On the other hand, a battery is basically constituted of battery cells each having output voltage of approximately 1V. For obtaining a high battery voltage, therefore, it is necessary to connect many battery cells in series. To avoid this, it is demanded, on the contrary to the above demand, that the battery voltage is made as low as possible.
In view of the above situation, it has been proposed to increase a battery voltage by means of a boost converter and thereafter input it to an inverter. With this arrangement, it is possible to set a high inverter input voltage even if the available battery voltage is low.
FIG. 6
shows one example of such a conventional motor drive circuit including a converter. A positive terminal of a battery
10
is connected to a converter
12
that includes a coil L and transistors Q
1
, Q
2
. One end of the coil L is connected to the positive terminal of the battery
10
. An emitter of the transistor Q
1
is connected to the other end of the coil L while a collector thereof is connected to a positive output line of the converter
12
(a positive bus bar of an inverter), and a collector of the transistor Q
2
is connected to the same end of the coil L and the emitter of the transistor Q
1
while an emitter thereof is connected to a negative terminal of the battery
10
(a negative output line of the converter
12
connected to a negative bus-bar of the inverter). Further, diodes D
1
, D
2
are respectively connected between the emitter and the collector of the transistors Q
1
, Q
2
, so as to allow the current to flow therethrough only in one direction from the emitter side to the collector side.
The transistors Q
1
, Q
2
are switched on/off alternately to change an “ON” time ratio therebetween as needed for achieving a desired high output voltage of the converter
12
.
Besides, a smoothing capacitor C is arranged between the positive and negative output lines of the converter
12
so as to smooth the output of the converter
12
.
The positive and negative outputs of the converter
12
smoothed by the capacitor C are respectively input to the positive and negative bus bars of the inverter
14
. The inverter
14
includes six transistors Q
3
to Q
8
and is adapted to produce three different phase outputs. More specifically, the transistors Q
3
and Q
4
, the transistors Q
5
and Q
6
, and the transistors Q
7
and Q
8
are respectively connected to each other in series between the positive and negative bas bars, thus forming three phase arms. Each connecting point between the transistor located in the upper side of each phase arm, namely the transistor Q
3
, Q
5
, or Q
7
, and that located in the lower side thereof, namely the transistor Q
4
, Q
6
, or Q
8
, provides each phase output of the inverter
14
. Also, diodes D
3
to D
8
are respectively connected between the emitter and the collector of the transistors Q
3
to Q
8
so as to allow the current to flow therethrough only in one direction from the emitter side to the collector side.
Each of the three phase outputs of the inverter
14
is connected to one end of a corresponding one of phase coils of a three-phase AC motor
16
(hereinafter will be simply referred to as “motor
16
”).
With the motor drive circuit constructed as described above, when driving the motor
16
, necessary one or ones of the transistors Q
3
to Q
8
are switched on such that the transistors in the upper side of the respective phase arms and the transistors in the lower side thereof are not ON at the same time, thus applying three phase currents shifted by 120° from one another to the motor
16
.
In this circuit, there also provided voltage sensors
20
a
,
20
b
,
22
a
and
22
b
, and current sensors
24
a
,
24
b
and
24
c
. The voltage sensors
20
a
,
20
c
are both used for detecting the voltage of the battery
10
(battery voltage: converter input voltage) while the voltage sensors
22
a
,
22
b
are both used for detecting the voltage of the capacitor C (converter output voltage: inverter input voltage). The current sensors
24
a
,
24
b
, and
24
c
are used for detecting the respective phase currents applied to the motor
16
. The detected values of these sensors and command values for controlling the motor output are input to the control unit
26
. In accordance with these values, the control unit
26
switches on/off the transistor Q
1
in the upper side of the converter
12
and the transistor Q
2
in the lower side thereof so as to obtain a desired output voltage of the converter
12
, while switching on/off the transistors Q
3
to Q
8
of the inverter
14
so as to bring the output of the motor
16
to a motor output command value.
The operations of the converter
12
and the inverter
14
are both controlled using a so-called PWM (Pulse Wave Modulation) control. More specifically, a desired voltage command value is set with respect to a predetermined triangular carrier (wave), and the duty ratio between the transistors Q
1
, Q
2
is adjusted to control the voltage conversion (i.e. voltage increase rate or voltage decrease rate).
On the other hand, when controlling the output of the motor
16
, the transistors Q
3
to Q
8
of the inverter
14
are switched on/off according to a result of a comparison between a voltage command value for the phase outputs and the predetermined triangular carrier (wave), so as to achieve the voltage command value.
In the motor drive circuit shown in
FIG. 6
, as described above, there also provided two voltage sensors
20
a
,
20
b
for detecting the voltage of the battery
10
and another two voltage sensors
22
a
,
22
b
for detecting the voltage of the capacitor C. This is because it is necessary to detect the input and output voltages of the converter
12
and to detect the input voltage of the inverter
14
for controlling their operations. With the two voltage sensors (
20
a
and
20
b
, or
22
a
and
22
b
) provided in each location, further, the voltage can be reliably detected even in the event of a failure of each voltage sensor.
More specifically, having two voltage sensors in each location as above makes it possible to detect the voltage even when one of the sensors fails, and thus provides the fail-safety of the system. However, such arrangement involves a problem that the overall cost of the system becomes high since four sensors are needed. Also, such arrangement may further cause the following problems. That is, the converter
12
becomes uncontrollable when the voltage sensors
20
a
,
20
b
for detecting the voltage of the battery
10
both fail, and the converter
12
and the inverter
14
both become uncontrollable when the voltage sensors
22
a
,
22
b
for detecting the voltage of the capacitor
Riley Shawn
Toyota Jidosha & Kabushiki Kaisha
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